1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive tape with improved room temperature handleability comprising at least one adhesive layer with at least one exposed surface and optionally a backing, wherein the pressure-sensitive adhesive layer comprises an epoxy/polyester based pressure-sensitive adhesive which is crosslinkable upon exposure to actinic or e-beam irradiation. The invention furthermore refers to a method of bonding a first substrate to a second substrate by using such pressure-sensitive adhesive tape and to the assembly prepared by such method.
2. Description of the Related Art
U.S. Pat. No. 4,920,182 describes UV-activatable curable compositions comprising one or more epoxy resins having an average of at least two 1,2-epoxy groups per molecule, one or more flexible polyesters which are terminated by, on average, at least two carboxyl groups, and a metallocene complex initiator. The composition, which can be used for the production of surface coatings on a variety of substrates or as an adhesive, can be cured by the application of heat or with a combination of irradiation and heat. The curing temperature is generally 40-200.degree. C., preferably 80-110.degree. C.
U.S. Pat. No. 4,256,828 describes photocopolymerizable compositions which contain epoxides, organic material with hydroxyl functionality such as hydroxyl-terminated polyesters, and a photosensitive aromatic sulfonium or iodonium salt of a halogen-containing complex ion. The compositions can be used in a variety of applications, for example, as photocurable ink vehicles, binders for abrasive particles, paints, adhesives, coatings for lithographic and relief printing plates, protective coatings for metals, wood, etc. The compositions are typically coated onto the respective surface, and are photocurable at room temperature or below.
The curable hot melt compositions of European Patent Publication No. 0,620,259 comprise an epoxy component, a polyester component, a photoinitiator and optionally a hydroxyl-containing material. The hot melt compositions, which can be tacky or non-tacky, may be applied to a variety of substrates by extruding, spraying, gravure printing or coating (e.g. by using a coating die, a heated knife blade coater, a roll coater or a reverse roll coater). The hot melt composition may also be applied as an uncured, free-standing adhesive film which, when used to bond a first substrate, may be irradiated on one or both sides and then placed between two substrates by the use of heat, pressure or both heat and pressure to bond the film to the two substrates. Alternatively, it is possible to laminate the hot melt adhesive film to a backing at room temperature using a pressure of, for example, 10 psi as is suggested in U.S. Pat. No. 5,436,063. This reference describes a coated abrasive article comprising a backing, a first binder on the backing, a plurality of abrasive particles in the first binder, and a second binder over the first binder and the abrasive particles. The first binder is a photocurable hot-melt adhesive as described in European Patent Publication No. 0,620,259.
While the crosslinkable hot melt epoxy/polyester based adhesives described above have broad utility, there are certain, specific applications where improved mechanical integrity and/or cohesive strength are desired or required. Therefore there is a need for a crosslinkable epoxy/polyester based pressure-sensitive adhesive materials available to the person skilled in the art to allow him or her to select appropriate adhesive materials exhibiting advantageous properties for a specific application and, in particular, for the preparation of unsupported and supported pressure-sensitive adhesive tapes with improved and/or convenient handleability at room temperature or below. Other objects of the present invention can be taken from the detailed specification below.